I would abandon my gear only if I were trapped or hung up on it, or it somehow hindered my escape.
If a bear has one end, he gets it.
A two-legged snake robs me.
If there is a fire, landslide or the like that requires instant reaction and exit.
That is why I carry my pocket survival kit:
The other scenario I have thought about is going for help to rescue another person. I would take essentials, emergency shelter, water, a little food, and extra clothing. So I leave the other person with my main shelter and sleeping bag, and take a water container, MicroPur tablets, a poncho and/or emergency bivy sack, knife, signaling gear, map, compass, fire starters, hat/gloves/warm layer, LED light, no-cook foods. This can all be carried in a stuff sack if needed. I want to be able to travel light and fast to get help for my sick/injured/trapped companion, but I want to insure my survival too.
After the Katrina disaster, I remember talking about how to survive something like that. Any backpacker could walk out of a post-hurricane mess, IF they had their kit. Walking from New Orleans to a safer place wouldn't be much of a challenge, local law-enforcement issues aside. Of course, the recent earthquakes in New Zealand and Japan bring this to mind, particularly when living on the other major subduction zone on the Ring of Fire.